Proximity Detection Using Adaptive Mutual Coupling Cancellation

ABSTRACT

An apparatus is disclosed for proximity detection using adaptive mutual coupling cancellation. In an example aspect, the apparatus includes at least two antennas, a wireless transceiver connected to the at least two antennas, and a mutual coupling cancellation module. The at least two antennas include a first antenna and a second antenna, which are mutually coupled electromagnetically. The second antenna includes two feed ports. The wireless transceiver is configured to transmit a radar transmit signal via the first antenna and receive two versions of a radar receive signal respectively via the two feed ports of the second antenna. The wireless transceiver is also configured to adjust a transmission parameter based on a decoupled signal. The transmission parameter varies based on a range to the object. The mutual coupling cancellation module is configured to generate the decoupled signal based on the two versions of the radar receive signal.

TECHNICAL FIELD

This disclosure relates generally to wireless transceivers and, morespecifically, to cancelling interference between at least two antennas.Certain embodiments enable and provide techniques for cancellinginterference for antennas that are mutually coupled electromagneticallyand are being used for proximity detection.

INTRODUCTION

To increase transmission rates and throughput, cellular and otherwireless networks are using signals with higher frequencies and smallerwavelengths. As an example, fifth generation (5G)-capable devicescommunicate with networks using frequencies that include those at ornear the extremely-high frequency (EHF) spectrum (e.g., frequenciesgreater than 25 gigahertz (GHz)) with wavelengths at or near millimeterwavelengths. These signals have various technological challenges, suchas higher path loss as compared to signals for earlier generations ofwireless communications. In certain scenarios it can be difficult for a5G wireless signal to travel far enough to make cellular communicationsfeasible at these higher frequencies.

Transmit power levels can be increased or beamforming can concentrateenergy in a particular direction to compensate for the higher path loss.These types of compensation techniques, however, increase powerdensities. The Federal Communications Commission (FCC) has determined amaximum permitted exposure (MPE) limit to accommodate these higher powerdensities. To meet targeted guidelines based on this MPE limit, devicesbalance performance with transmission power and other considerations.This balancing act can be challenging to realize given cost, size,functional design objectives and/or involved constraints.

BRIEF SUMMARY

The following summarizes some aspects of the present disclosure toprovide a basic understanding of the discussed technology. This summaryis not an extensive overview of all contemplated features of thedisclosure, and is intended neither to identify key or critical elementsof all aspects of the disclosure nor to delineate the scope of any orall aspects of the disclosure. Its sole purpose is to present someconcepts of one or more aspects of the disclosure in summary form as aprelude to the more detailed description that is presented later.

An apparatus is disclosed that implements proximity detection usingadaptive mutual coupling cancellation. The described techniques utilizean existing wireless transceiver and antennas within a computing deviceto transmit and receive radar signals and determine a range (e.g., adistance or slant range) to an object. Due to a proximity of theantennas with respect to each other, the antennas areelectromagnetically mutually coupled such that energy can leak between atransmitting antenna and a receiving antenna. To detect the object inthe presence of this self-made interference, a mutual couplingcancellation module combines at least two receive signals in such a wayas to suppress or attenuate the mutual coupling interference. The atleast two receive signals can be obtained from at least two feed portsthat are associated with a same antenna or different antennas.

Two described example implementations of the mutual couplingcancellation module utilize a zero-forcing combiner module or areciprocal cancellation module to process the at least two receivesignals. A decoupled signal can be produced by suppressing the mutualcoupling interference and thereby enabling weak reflections of the radarsignal to be analyzed for proximity detection. Based on this analysis, atransmission parameter that is used for wireless communication can beadjusted to enable the wireless transceiver to meet guidelinespromulgated by the government or the wireless industry, such as aMaximum Permitted Exposure (MPE) limit as determined by the FederalCommunications Commission (FCC). By actively measuring the range to anobject, a surrounding environment can be continually monitored and thetransmission parameter can be incrementally adjusted to account formovement by the object.

In an example aspect, an apparatus is disclosed. The apparatus includesat least two antennas, a wireless transceiver connected to the at leasttwo antennas, and a mutual coupling cancellation module. The at leasttwo antennas include a first antenna and a second antenna. The secondantenna includes two feed ports. The first antenna and the secondantenna are mutually coupled electromagnetically. The wirelesstransceiver is configured to transmit a radar transmit signal via thefirst antenna and receive two versions of a radar receive signalrespectively via the two feed ports of the second antenna. The radarreceive signal comprises a reflected component corresponding to areflection of the radar transmit signal via an object and a mutualcoupling component corresponding to a transmission of the radar transmitsignal via the first antenna. The wireless transceiver is alsoconfigured to adjust a transmission parameter based on a decoupledsignal. The transmission parameter varies based on a range to theobject. The mutual coupling cancellation module is connected to the twofeed ports and is configured to generate the decoupled signal based onthe two versions of the radar receive signal.

In an example aspect, an apparatus is disclosed. The apparatus includesat least two antennas and a wireless transceiver connected to the atleast two antennas. The at least two antennas include a first antennaand a second antenna. The first antenna and at least the second antennaare mutually coupled electromagnetically. The wireless transceiver isconfigured to transmit a radar transmit signal via the first antenna andreceive multiple versions of a radar receive signal via multiple feedports including at least one feed port of the second antenna. The radarreceive signal comprises a reflected component corresponding to areflection of the radar transmit signal via an object and a mutualcoupling component corresponding to a transmission of the radar transmitsignal via the first antenna. The wireless transceiver is alsoconfigured to adjust a transmission parameter based on a decoupledsignal. The transmission parameter varies based on a range to theobject. The apparatus also includes a mutual coupling cancellationcircuit connected to the multiple feed ports. The mutual couplingcancellation circuit is configured to generate the decoupled signalbased on the multiple versions of the radar receive signal such that themutual coupling component is suppressed.

In an example aspect, a method for proximity detection using adaptivemutual coupling cancellation is disclosed. The method includestransmitting a radar transmit signal via a first antenna and receivingmultiple versions of a radar receive signal via multiple feed portsincluding at least one feed port of a second antenna. The first antennaand the second antenna are mutually coupled electromagnetically. Theradar receive signal comprises a reflected component corresponding to areflection of the radar transmit signal via an object and a mutualcoupling component corresponding to a transmission of the radar transmitsignal via the first antenna. The method also includes generating adecoupled signal by processing the multiple versions of the radarreceive signal such that the mutual coupling component is attenuated.Based on the decoupled signal, the method includes adjusting atransmission parameter, which is varied according to a range to theobject.

In an example aspect, an apparatus is disclosed. The apparatus includesat least two antennas and a mutual coupling cancellation module. The atleast two antennas include a first antenna and a second antenna. Thesecond antenna includes multiple feed ports. The first antenna isconfigured to generate radiation. The first antenna and the secondantenna are mutually coupled electromagnetically. The second antenna isconfigured to generate multiple versions of a radio-frequency signalrespectively via the multiple feed ports, with the multiple versions ofthe radio-frequency signal including interference indicative of theradiation generated by the first antenna. The mutual couplingcancellation module includes a zero-forcing combiner module and areciprocal cancellation module. The zero-forcing combiner module isconfigured to combine interference null-space projections of themultiple versions of the radio-frequency signal to attenuate theinterference. The reciprocal cancellation module is configured to scalea version of the multiple versions of the radio-frequency signal toproduce a scaled signal and to subtract the scaled signal from anotherversion of the multiple versions of the radio-frequency signal toattenuate the interference.

Other aspects, features, and embodiments of the technology will becomeapparent to those of ordinary skill in the art, upon reviewing thefollowing description of specific, exemplary embodiments in conjunctionwith the accompanying figures. While features of the technologydiscussed below may be described relative to certain embodiments andfigures below, all embodiments can include one or more of theadvantageous features discussed. While one or more embodiments may bediscussed as having certain advantageous features, one or more of suchfeatures may also be used in accordance with the various embodimentsdiscussed. In similar fashion, while exemplary embodiments may bediscussed below as device, system, or method embodiments it should beunderstood that such exemplary embodiments can be implemented in varyingshapes, sizes, layouts, arrangements, circuits, devices, systems, andmethods.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates an example computing device for proximity detectionusing adaptive mutual coupling cancellation.

FIG. 2 illustrates an example operating environment for proximitydetection using adaptive mutual coupling cancellation.

FIG. 3 illustrates an example sequence flow diagram for proximitydetection using adaptive mutual coupling cancellation.

FIG. 4 illustrates multiple examples of an antenna for proximitydetection using adaptive mutual coupling cancellation.

FIG. 5 illustrates an example antenna array for proximity detectionusing adaptive mutual coupling cancellation.

FIG. 6 illustrates an example wireless transceiver, mutual couplingcancellation module, and processor for proximity detection usingadaptive mutual coupling cancellation.

FIG. 7 illustrates an example scheme performed by a mutual couplingcancellation module for proximity detection using adaptive mutualcoupling cancellation.

FIG. 8 illustrates an example scheme performed by a zero-forcingcombiner module for proximity detection using adaptive mutual couplingcancellation.

FIG. 9 illustrates an example scheme performed by a reciprocalcancellation module for proximity detection using adaptive mutualcoupling cancellation.

FIG. 10-1 is a flow diagram illustrating an example process forproximity detection using adaptive mutual coupling cancellation.

FIG. 10-2 is a flow diagram illustrating another example process forproximity detection using adaptive mutual coupling cancellation.

FIG. 11-1 is a flow diagram illustrating yet another example process forproximity detection using adaptive mutual coupling cancellation.

FIG. 11-2 is a flow diagram illustrating still another example processfor proximity detection using adaptive mutual coupling cancellation.

DETAILED DESCRIPTION

Current high-frequency and small-wavelength communications struggle tobalance performance with a need to meet the Federal CommunicationsCommission's maximum permitted exposure limit (e.g., the FCC's MPElimit). This struggle can prevent devices from taking full advantage ofincreased data rates (e.g., those enabled by 5G wirelesscommunications). Because the MPE limit is affected by the proximity of auser to a device's antenna, however, techniques described in thisdocument enable greater wireless performance while staying within theFCC's MPE limit. To do so, these techniques detect a user's proximity toa device. Based on the detected proximity, the device can balance apower density of transmitted wireless signals with the requirement tomeet the MPE limit. As a result, the device is permitted to transmitwireless signals with higher average power levels, which enables thewireless signals to travel farther, such as between a smart phone and aremote cellular base station.

Some proximity-detection techniques may use a dedicated sensor to detectthe user, such as a camera or an infrared sensor. However, these sensorsmay be bulky or expensive. Furthermore, a single electronic device caninclude multiple antennas that are positioned on different surfaces(e.g., on a top, a bottom, or opposite sides). To account for each ofthese antennas, multiple cameras or sensors may need to be installednear each of these antennas, which further increases a cost and size ofthe electronic device.

In contrast, techniques for proximity detection using adaptive mutualcoupling cancellation are described herein. The described techniquesutilize an existing wireless transceiver and antennas within a computingdevice to transmit and receive radar signals and determine a range(e.g., a distance or slant range) to an object. Due to a proximity ofthe antennas with respect to each other, the antennas are mutuallycoupled such that energy can leak between a transmitting antenna and areceiving antenna. To detect the object in the presence of thisself-made interference, a mutual coupling cancellation module processingat least two receive signals in such a way as to suppress or attenuatethe mutual coupling. The at least two receive signals can be obtainedfrom at least two feed ports that are associated with a same antenna ordifferent antennas.

Two described implementations of the mutual coupling cancellation moduleutilize a zero-forcing combiner module or a reciprocal cancellationmodule to process the at least two receive signals. The mutual couplingcancellation results in a decoupled signal that enables weak reflectionsof the radar signal to be analyzed for proximity detection. Based onthis analysis, a transmission parameter that is used for wirelesscommunication can be adjusted to enable the wireless transceiver to meetguidelines promulgated by the government or the wireless industry, suchas a Maximum Permitted Exposure (MPE) limit as determined by the FederalCommunications Commission (FCC). Further, by actively measuring therange to an object, a surrounding environment can be continuallymonitored and the transmission parameter can be incrementally adjustedto account for movement by the object.

Some embodiments may offer a relatively inexpensive approach that canutilize existing transceiver hardware and antennas. The mutual couplingcancellation module marginally impacts a design of the wirelesstransceiver and can be implemented in software or hardware. Thedescribed techniques need not utilize a calibration procedure ortraining sequence (e.g., those involving a characterization of a mutualcoupling channel). Instead, estimations of the mutual coupling channeloccur in real-time, thereby enabling responsive adaptation to variouschanges in antenna impedance or load variations. Such variations canoccur due to a proximity of a user's hand to an antenna, solar loading,and so forth. With this adaptive capability, proximity detection can beperformed using a variety of different antenna designs or antenna arrayconfigurations.

In some implementations, the wireless transceiver may be utilized instand-alone proximity-detection applications. For example, the wirelesstransceiver can be implemented as an automotive bumper sensor to assistwith parking or autonomous driving. As another example, the wirelesstransceiver can be installed on a drone to provide collision avoidance.In other implementations, the wireless transceiver can selectivelyperform proximity detection or wireless communication. In such cases,this enables dual-use of components within the transmit and receivechains of a wireless transceiver of a computing device, which decreasescost and size of the wireless transceiver, as well as the computingdevice. Based on the proximity detection, and as described herein,transmission parameters can be adjusted for wireless communication toenable the wireless transceiver to meet safety guidelines promulgated bythe government or the wireless industry, such as a Maximum PermittedExposure (MPE) limit as determined by the Federal CommunicationsCommission (FCC).

While aspects and embodiments are described in this application byillustration to some examples, those skilled in the art will understandthat additional implementations and use cases may come about in manydifferent arrangements and scenarios. Innovations described herein maybe implemented across many differing platform types, devices, systems,shapes, sizes, packaging arrangements. For example, embodiments and/oruses may come about via integrated chip embodiments and othernon-module-component based devices (e.g., end-user devices, vehicles,communication devices, computing devices, industrial equipment,retail/purchasing devices, medical devices, artificial intelligence(AI)-enabled devices, etc.). While some examples may or may not bespecifically directed to use cases or applications, a wide assortment ofapplicability of described innovations may occur. Implementations mayrange a spectrum from chip-level or modular components to non-modular,non-chip-level implementations and further to aggregate, distributed, ororiginal equipment manufacturer (OEM) devices or systems incorporatingone or more aspects of the described innovations. In some practicalsettings, devices incorporating described aspects and features may alsonecessarily include additional components and features forimplementation and practice of claimed and described embodiments. Forexample, transmission and reception of wireless signals necessarilyincludes a number of components for analog and digital purposes (e.g.,hardware components including antenna, radio-frequency (RF)-chains,power amplifiers, modulators, buffer, processor(s), interleaver,adders/summers, etc.). It is intended that innovations described hereinmay be practiced in a wide variety of devices, chip-level components,systems, distributed arrangements, end-user devices, etc. of varyingsizes, shapes, and constitutions.

FIG. 1 illustrates an example computing device 102 for proximitydetection using adaptive mutual coupling cancellation. In an exampleenvironment 100, the computing device 102 communicates with a basestation 104 through a wireless communication link 106 (wireless link106). In this example, the computing device 102 is implemented as asmart phone or sometimes known as a user equipment/terminal. However,the computing device 102 may be implemented as any suitable computing orelectronic device, such as a modem, cellular base station, broadbandrouter, access point, cellular phone, gaming device, navigation device,media device, laptop computer, desktop computer, tablet computer,server, network-attached storage (NAS) device, smart appliance or otherinternet of things (IoT) device, medical device, vehicle-basedcommunication system, radio apparatus, entertainment device, wearable,implantable, pharmaceutical device, and so forth.

The base station 104 communicates with the computing device 102 via thewireless link 106, which may be implemented as any suitable type ofwireless link. Although depicted as a tower of a cellular network, thebase station 104 may represent or be implemented as another device, suchas a satellite, cable television head-end, terrestrial televisionbroadcast tower, access point, peer-to-peer device, mesh network node,small cell node, fiber optic line, and so forth. Therefore, thecomputing device 102 may communicate with the base station 104 oranother device via a wired connection, a wireless connection, or acombination thereof.

The wireless link 106 can include a downlink of data or controlinformation communicated from the base station 104 to the computingdevice 102 and an uplink of other data or control informationcommunicated from the computing device 102 to the base station 104. Thewireless link 106 may be implemented using any suitable communicationprotocol or standard, such as 3rd Generation Partnership ProjectLong-Term Evolution (3GPP LTE), 5th Generation (5G), IEEE 802.11, IEEE802.16, Bluetooth™, and so forth. In some implementations, instead of orin addition to providing a data link, the wireless link 106 maywirelessly provide power and the base station 104 may comprise a powersource.

As shown, the computing device 102 includes an application processor 108and a computer-readable storage medium 110 (CRM 110). The applicationprocessor 108 may include any type of processor that executesprocessor-executable code stored by the CRM 110. The CRM 110 may includeany suitable type of data storage media, such as volatile memory (e.g.,random access memory (RAM)), non-volatile memory (e.g., Flash memory),optical media, magnetic media (e.g., disk or tape), and so forth. In thecontext of this disclosure, the CRM 110 is implemented to storeinstructions 112, data 114, and other information of the computingdevice 102, and thus does not include transitory propagating signals orcarrier waves.

The computing device 102 may also include input/output ports 116 (I/Oports 116) and a display 118. The I/O ports 116 enable data exchanges orinteraction with other devices, networks, or users. The I/O ports 116may include serial ports (e.g., universal serial bus (USB) ports),parallel ports, audio ports, infrared (IR) ports, and so forth. Thedisplay 118 presents graphics of the computing device 102, such as auser interface associated with an operating system, program, orapplication. Alternately or additionally, the display 118 may beimplemented as a display port or virtual interface, through whichgraphical content of the computing device 102 is presented.

A wireless transceiver 120 of the computing device 102 providesconnectivity to networks and/or other electronic wireless devices.Additionally, the computing device 102 may include a wired transceiver,such as an Ethernet or fiber optic interface for communicating over alocal network, intranet, or the Internet. The wireless transceiver 120may facilitate communication over any suitable type of wireless network,such as a wireless LAN (WLAN), peer-to-peer (P2P) network, mesh network,cellular network, wireless wide-area-network (WWAN), and/or wirelesspersonal-area-network (WPAN). In the context of the example environment100, the wireless transceiver 120 enables the computing device 102 tocommunicate with the base station 104 and networks connected therewith.

The wireless transceiver 120 includes circuitry and logic fortransmitting and receiving signals via two or more antennas 126.Components of the wireless transceiver 120 can include amplifiers,mixers, switches, analog-to-digital converters, filters, and so forthfor conditioning signals. The wireless transceiver 120 may also includelogic to perform in-phase/quadrature (I/Q) operations, such assynthesis, encoding, modulation, decoding, demodulation, and so forth.In some cases, components of the wireless transceiver 120 areimplemented as separate transmitter and receiver entities. Additionallyor alternatively, the wireless transceiver 120 can be realized usingmultiple or different sections to implement respective transmitting andreceiving operations (e.g., separate transmit and receive chains).

The computing device 102 also includes a mutual coupling (MC)cancellation module 122. The mutual coupling cancellation module 122 canbe connected to a wireless transceiver 120 and a processor 124. As usedherein, the term “connect” or “connected” refers to an electricalconnection, including a direct connection (e.g., connecting discretecircuit elements via a same node) or an indirect connection (e.g.,connecting discrete circuit elements via one or more other devices orother discrete circuit elements). The mutual coupling cancellationmodule 122 and the processor 124 can be respectively implemented withinor separate from the wireless transceiver 120. The mutual couplingcancellation module 122 can be implemented in software or hardware. Insome instances, the mutual coupling cancellation module 122 can beincorporated in or realized using software, firmware, hardware, fixedlogic circuitry, or combinations thereof. The mutual couplingcancellation module 122 can be implemented within an integrated circuitor as part of the processor 124 or other electronic component of thecomputing device 102. In some implementations, the processor 124 mayexecute computer-executable instructions that are stored within the CRM110 to implement the mutual coupling cancellation module 122. Inoperation, the mutual coupling cancellation module 122 can cancelself-made interference (e.g., interference due to mutual coupling) toenable detection of relatively weak reflections that are analyzed forproximity detection. Thus, the mutual coupling cancellation module 122can at least partially implement proximity detection using adaptivemutual coupling cancellation, as described in FIGS. 6-9.

The processor 124, which can be implemented as a modem or part of amodem, controls the wireless transceiver 120 and enables wirelesscommunication or proximity detection to be performed. The processor 124can include a portion of the CRM 110 or can access the CRM 110 to obtaincomputer-readable instructions. The processor 124 can include basebandcircuitry to perform high-rate sampling processes that can includeanalog-to-digital conversion, digital-to-analog conversion, Fouriertransforms, gain correction, skew correction, frequency translation, andso forth. The processor 124 can provide communication data to thewireless transceiver 120 for transmission. The processor 124 can alsoprocess a baseband version of a signal obtained from the wirelesstransceiver 120 to generate data, which can be provided to other partsof the computing device 102 via a communication interface for wirelesscommunication or proximity detection.

The wireless transceiver 120 can also include a controller (not shown),e.g., to realize the mutual coupling cancellation module 122. Thecontroller can include at least one processor and CRM, which storescomputer-executable instructions (such as the application processor 108,the CRM 110, and the instructions 112). The processor and the CRM can belocalized at one module or one integrated circuit chip or can bedistributed across multiple modules or chips. Together, a processor andassociated instructions can be realized in separate circuitry, fixedlogic circuitry, hard-coded logic, and so forth. The controller can beimplemented as part of the wireless transceiver 120, the processor 124,the application processor 108, a special-purpose processor configured toperform MPE techniques, a general-purpose processor, some combinationthereof, and so forth.

FIG. 2 illustrates an example operating environment 200 for proximitydetection using adaptive mutual coupling cancellation. In the exampleenvironment 200, a hand 214 of a user holds the computing device 102. Inone aspect, the computing device 102 communicates with the base station104 by transmitting an uplink signal 202 (UL signal 202) or receiving adownlink signal 204 (DL signal 204) via the two or more antennas 126. Auser's thumb, however, can represent a proximate object 206 that may beexposed to radiation via the uplink signal 202.

To detect whether the object 206 exists or is within a detectable range,the computing device 102 transmits a radar transmit signal 208 via atleast one of the antennas 126 and receives a radar receive signal 210via at least another one of the antennas 126. In some cases, the radarreceive signal 210 can be received during a portion of time that theradar transmit signal 208 is transmitted. The radar transmit signal 208can be implemented as a frequency-modulated continuous-wave (FMCW)signal or a frequency-modulated pulsed signal. The type of frequencymodulation can include a linear frequency modulation, a triangularfrequency modulation, a sawtooth frequency modulation, and so forth.Based on the radar receive signal 210, the range to the object 206 canbe determined.

In FIG. 2, the radar receive signal 210 is shown to include both areflected signal 218 and a mutual coupling signal 216. The reflectedsignal 218 includes a portion of the radar transmit signal 208 that isreflected by the object 206, and the mutual coupling signal 216 includesanother portion of the radar transmit signal 208 that is not reflectedby the object 206. A propagation distance between the antennas 126 andthe object 206 and a partial absorption of the radar transmit signal 208via the object 206 causes the reflected signal 218 to be weaker relativeto the mutual coupling signal 216. The reflected signal 218 may alsohave a different phase or frequency relative to the radar transmitsignal 208 and the mutual coupling signal 216 based on reflectionproperties or motion of the object 206. In general, the reflected signal218 contains information that can be used for detecting the object 206and for determining a range to the object 206.

The mutual coupling signal 216 exists within the radar receive signal210 due to a direct or indirect coupling between the antennas 126 (e.g.,the antennas 126 are mutually coupled). In the depicted configuration,the antennas 126 are co-located or otherwise proximate to one another.Due to this proximity, the antennas 126 are mutually coupledelectromagnetically such that a portion of the energy that is radiatedvia one of the antennas 126 generates interference that makes itchallenging to detect the reflected signal 218 due to the mutualcoupling signal 216.

The antennas 126 may be arranged via modules and may have a variety ofconfigurations. For example, the antennas 126 may comprise at least twodifferent antennas, at least two antenna elements of an antenna array212 (as shown towards the bottom of FIG. 2), at least two antennaelements associated with different antenna arrays, or any combinationthereof. The antenna array 212 is shown to include multiple antennas126-1 to 126-N, where N represents a positive integer greater than one.Further, the array 212 may be arranged in multi-dimensional arrays.Additionally or alternatively, the array 212 may be configured for beammanagement techniques, such as beam determination, beam measurement,beam reporting, or beam sweeping. A distance between the antennas 126within the antenna array 212 can be based on frequencies that thewireless transceiver 120 emits. For example, the antennas 126 can bespaced apart by approximately half a wavelength from one another (e.g.,by approximately half a centimeter (cm) apart for frequencies around 30GHz). The antennas 126 may be implemented using any type of antenna,including patch antennas, dipole antennas, bowtie antennas, or acombination thereof, as further described with respect to FIGS. 3 and 4.

Consider, for example, the antennas 126 as comprising the first antenna126-1 and the second antenna 126-2 of the antenna array 212. The firstantenna 126-1 transmits the radar transmit signal 208, and the secondantenna 126-2 receives the radar receive signal 210. The mutual couplingbetween the antennas 126 cause a portion of the radar transmit signal208, which is represented by the mutual coupling signal 216, to leakinto or be received by the second antenna 126-2. Because the mutualcoupling signal 216 is significantly stronger than the reflected signal218 (e.g., by approximately 25 dB or more), the mutual coupling signal216 can prevent the computing device 102 from detecting the object 206,absent implementation of a technique to cancel the mutual couplingcomponent. For example, the reflected signal 218 can be obscured bysidelobes of the mutual coupling signal 216. The mutual couplingcancellation module 122, however, attenuates the mutual coupling signal216 to enable the object 206 to be detected using the mutually-coupledantennas 126. Based on the proximity detection, a transmission parametercan be adjusted for use during wireless communication. An examplesequence for switching between wireless communication and proximitydetection is further described with respect to FIG. 3

FIG. 3 illustrates an example sequence flow diagram for proximitydetection using adaptive mutual coupling cancellation, with timeelapsing in a downward direction. Examples of a wireless communicationmode are shown at 302 and 306, and examples of a proximity detectionmode are shown at 304 and 308. The proximity detection modes can occurat fixed time intervals, between active data cycles that occur duringwireless communication, at predetermined times as set by the processor124, as part of an initialization process before wireless communicationsoccur, responsive to detection of device movement, or based onindications that the user may be proximate to the device (e.g., based onthe wireless transceiver 120 observing a decrease in power in a downlinksignal 204 or the application processor 108 determining that the user isinteracting with the display 118 of the computing device 102).

At 302, the wireless transceiver 120 transmits a high-power (e.g.,normal) uplink signal 202-1 configured to provide sufficient range to adestination, such as a base station 104. After transmitting the uplinksignal 202-1, the radar transmit signal 208-1 is transmitted via thewireless transceiver 120 and the antennas 126 at 304. As describedabove, a radar transmit signal 208 enables the computing device 102 todetect an object 206 and determine if the object 206 is near thecomputing device 102. In this case, the radar transmit signal 208-1 isrepresented by a low-power wide-band signal. Based on a detection, thewireless transceiver 120 can adjust a transmission parameter for a nextuplink signal 202 to account for MPE compliance guidelines.

The proximity detection mode can also determine the range to the object206, thereby enabling transmission of the uplink signal 202 to complywith range-dependent guidelines, such as a maximum power density.Because power density is proportional to transmit power and inverselyproportional to range, an object 206 at a closer range is exposed to ahigher power density than another object 206 at a farther range for asame transmit power level. Therefore, a similar power density at theobject 206 can be achieved by increasing the transmit power level if theobject 206 is at a farther range and decreasing the transmit power levelif the object 206 is at a closer range. In this way, the wirelesstransceiver 120 can adjust transmission of the uplink signal 202 toenable the power density at the object 206 for both the closer range andthe farther range to be below the maximum power density. At the sametime, because the range is known, the transmit power level can beincreased to a level that facilitates wireless communication andcomports with the compliance guideline.

At 306, the wireless transceiver 120 transmits a next uplink signal 202.In the depicted example, a high-power uplink signal 202-2 is transmittedif an object 206 is not detected. Alternatively, a low-power uplinksignal 202-3 is transmitted if the object 206 is detected. The lowtransmit power can be, for example, between approximately five andtwenty decibel-milliwatts (dBm) less than the high-power signal at 302.In addition to or instead of changing a power of the next uplink signal202, the uplink signal 202 can be transmitted using a different antennawithin the computing device 102 or using a different beam steering angle(e.g., different than the antennas 126 or the beam steering angle usedfor transmitting the uplink signal 202-1 at 302). Although not shown,the wireless transceiver 120 can alternatively skip the wirelesscommunication mode at 306 and perform another proximity detection modeusing another antenna or a different transmit power level to detectobjects 206 at various locations or distances around the computingdevice 102.

At 308, the wireless transceiver 120 and antennas 126 transmit anotherradar transmit signal 208-2 to attempt to detect the object 206. Byscheduling multiple radar transmit signals 208 over some time period,transmission of the uplink signal 202 can be dynamically adjusted basedon a changing environment or movement by the object 206. Furthermore,appropriate adjustments can be made to balance communication performancewith compliance or radiation requirements.

The sequence described above can also be applied to othermutually-coupled antennas. The other antennas and the antennas 126 maytransmit multiple radar transmit signals 208 sequentially or inparallel. To enable proximity detection through the use ofmutually-coupled antennas 126, the wireless transceiver 120 receives theradar receive signal 210 of FIG. 2 via at least two feed ports, whichare further described with respect to FIG. 4.

FIG. 4 illustrates an example antenna 126 for proximity detection usingadaptive mutual coupling cancellation and three example implementationsthereof. The example antenna 126 illustrated in FIG. 4 can be used toimplement either of the antennas 126 (e.g., a transmitting antenna or areceiving antenna). In general, the antenna 126 in FIG. 4 is describedwith respect to a receiving antenna 126. In the depicted configuration(in the top half of FIG. 4), the antenna 126 includes multiple feedports 402, such as a first feed port 402-1 and a second feed port 402-2.The response of the antenna 126 to the radar receive signal 210 isseparated into multiple versions 404, such as versions 404-1 and 404-2respectively obtained via the feed ports 402-1 and 402-2. Althoughsimilar, the multiple versions 404 of the radar receive signal 210 varydue to differences in a type of feed port 402 or differences due tolocation or orientation of the feed ports 402-1 and 402-2. Theseversions 404-1 and 404-2 are used by the mutual coupling cancellationmodule 122 to perform mutual coupling cancellation 410.

Three example types of antenna 126 are depicted towards the bottom ofFIG. 4. In one example, the antenna 126 comprises a dipole antenna 412,which includes a pair of differential feed ports 414 (e.g., a positive(+) feed port 414-1 and a negative (−) feed port 414-2). Thus, the feedports 402-1 and 402-2 can be implemented using the differential feedports 414-1 and 414-2 such that the versions 404-1 and 404-2 areout-of-phase with respect to each other (e.g., differ in phase byapproximately 180 degrees). As another example, the antenna 126comprises a patch antenna 416, which includes a horizontally-polarizedfeed port 418-1 and a vertically-polarized feed port 418-2. Accordingly,the versions 404-1 and 404-2 have orthogonal polarities if the feedports 402-1 and 402-2 are implemented using the polarized feed ports418. In this instance, the versions 404-1 and 404-2 respectivelyrepresent a horizontally-polarized version and a vertically-polarizedversion. As yet another example, the antenna 126 comprises a bowtieantenna 420, which includes directional feed ports 422-1 and 422-2. Inthis case, the versions 404-1 and 404-2 represent different angulardirections of the radar receive signal 210 that are sensed alongdifferent angles of arrival.

In FIG. 4, the feed ports 402 and the versions 404 of the radar receivesignal 210 are shown to be associated with the antenna 126.Alternatively or in addition to, the feed ports 402 and the versions 404may be obtained using two different antennas. In general, any type offeed port 402 (including the feed ports 414-1, 414-2, 418-1, 418-2,422-1, or 422-2) may be used to produce the multiple versions 404 if thefeed ports 402 are in some way different from one another (e.g., sensedifferent phases, polarizations, angles of arrivals, or are otherwiseassociated with different antennas that are placed at different physicallocations). By using multiple feed ports 402, the described techniquesfor proximity detection using adaptive mutual coupling cancellation canoperate without an extensive calibration process that characterizes amutual coupling channel (e.g., without determining a transmit powerassociated with the radar transmit signal 208 or explicitlycharacterizing the mutual coupling between the transmitting andreceiving antennas 126).

FIG. 5 illustrates an example antenna array 212 for proximity detectionusing adaptive mutual coupling cancellation. In the depictedconfiguration, the antenna array 212 is positioned in an upper-leftcorner of the computing device 102. To detect one or more objects 206(of FIG. 2) that are positioned differently with respect to thecomputing device 102, the antenna array 212 includes a combination offour dipole antennas 412-1, 412-2, 412-3, and 412-4 and four patchantennas 416-1, 416-2, 416-3, and 416-4. The dipole antennas 412-1 and412-2 can be used to detect an object 206 that is near a top 502 of thecomputing device 102 along a vertical direction or Y axis. Likewise, thedipole antennas 412-3 and 412-4 can detect another object 206 that isnear a side 504 of the computing device 102 along a horizontal directionor X axis. The patch antennas 416-1, 416-2, 416-3, or 416-4 can detectan additional object 206 that is in front 506 of the computing device102 or above the page along a Z axis.

In some implementations, the radar receive signal 210 (of FIGS. 2 and 4)may be sensed using a same antenna 126. For example, the dipole antenna412-2 can transmit the radar transmit signal 208 and the dipole antenna412-1 can generate the versions 404-1 and 404-2 of the radar receivesignal 210 via the corresponding feed ports 414-1 and 414-2 (of FIG. 4).As another example, the patch antenna 416-2 can transmit the radartransmit signal 208 and the patch antenna 416-1 can generate theversions 404-1 and 404-2 via the feed ports 418-1 and 418-2.

In other implementations, the radar receive signal 210 may be sensedusing different antennas 126. For example, the dipole antenna 412-2 cantransmit the radar transmit signal 208 and the dipole antennas 412-1 and412-3 can each respectively generate one of the versions 404-1 or 404-2.Alternatively, both dipole antennas 412-1 and 412-3 can respectivelygenerate both of the versions 404-1 and 404-2 via respective feed ports414-1 and 414-2. As another example, the patch antenna 416-2 cantransmit the radar transmit signal 208 and each of the patch antennas416-1 and 416-3 can respectively generate one of the versions 404-1 or404-2. Alternatively, both patch antennas 416-1 and 416-3 canrespectively generate both of the versions 404-1 and 404-2 viarespective feed ports 418-1 and 418-2.

Different types of antenna 126 can also be used to respectively transmitor receive the radar signals 208 or 210. For example, the dipole antenna412-2 can transmit the radar transmit signal 208, and each of the dipoleantenna 412-3 and the patch antenna 416-2 can respectively generate oneof the versions 404-1 or 404-2. In some cases, the dipole antenna 412-3or the patch antenna 416-2 can generate multiple versions 404 such thata total quantity of versions 404 is greater than two. Although notexplicitly depicted, multiple radar transmit signals 208 may also betransmitted simultaneously. For example, the dipole antenna 412-1 or412-2 can transmit a radar transmit signal 208 towards the top 502 ofthe computing device 102 while one of the patch antennas 416-1, 416-2,416-3, or 416-4 transmits another radar transmit signal 208 towards thefront 506 of the computing device 102.

By utilizing different types of antennas 126 or by having the antennas126 positioned at different locations within or around the computingdevice 102, multiple locations of the object 206 (or multiple objects206) can be monitored using the described techniques. This furtherenables transmission of the uplink signal 202 to be independentlyadjusted relative to which one or more antennas 126 detect the object206. Such independent detection therefore enables two or more of theantenna 126 to be configured for different purposes. For example one ofthe antennas 126 can be configured for enhanced communicationperformance while another one of the antennas 126 is simultaneouslyconfigured to comply with FCC requirements. As described in furtherdetail with respect to FIG. 6, some of the components of the wirelesstransceiver 120 can be utilized for both wireless communication andproximity detection.

FIG. 6 illustrates an example wireless transceiver 120, mutual couplingcancellation module 122, and processor 124 for proximity detection usingadaptive mutual coupling cancellation. The wireless transceiver 120includes a transmitter 602 and receivers 604-1 and 604-2, which arerespectively connected between the mutual coupling cancellation module122 and the antenna array 212. The transmitter 602 is shown to include asignal generator 606, a digital-to-analog converter (DAC) 608, a filter610-1 (e.g., a low-pass filter (LPF)), a mixer 612-1, and an amplifier614-1. The signal generator 606 can generate a digital transmit signal634, which may be used to derive the radar transmit signal 208 or theuplink signal 202 (of FIGS. 2 and 3). The transmitter 602 is connectedto at least one feed port 402-1 or 402-2 of the antenna 126-1, such asat least one of the differential feed ports 414 of the dipole antenna412, at least one of the polarized feed ports 418 of the patch antenna416, or at least one of the directional feed ports 422 of the bowtieantenna 420, as shown in FIG. 4.

The receivers 604-1 and 604-2 represent two parallel receive chainswithin the wireless transceiver 120 that are respectively connected totwo feed ports 402-1 and 402-2 (of FIG. 4) of the antenna 126-2.Although a single antenna 126-2 is shown to be connected to the tworeceive chains, the two receivers 604-1 and 604-2 can alternatively berespectively connected to two different antennas 126, such as the secondantenna 126-2 and the Nth antenna 126-N of FIG. 2. Each receive chainrespectively includes amplifiers 614-2 and 614-3 (e.g., low-noiseamplifiers), mixers 612-2 and 612-3, filters 610-2 and 610-3 (e.g.,LPFs), analog-to-digital converters (ADC) 616-1 and 616-2, and digitalmixers 618-1 and 618-2. The wireless transceiver 120 also includes alocal oscillator 620, which generates a reference signal enabling themixers 612-1, 612-2, and 612-3 to upconvert or downconvert analogsignals within the transmit or receive chains. The transmitter 602 andthe receivers 604-1 and 604-2 can also include other additionalcomponents that are not depicted in FIG. 6 such as band-pass filters,additional mixers, switches, and so forth.

Using these components, the wireless transceiver 120 can transmit theuplink signal 202 or receive the downlink signal 204 (of FIGS. 2 and 3)for wireless communications. For proximity detection, the transmitter602 generates the radar transmit signal 208 via the antenna 126-1, andthe receivers 604-1 and 604-2 receive different versions 404 of theradar receive signal 210 via the antenna 126-2. The response of theantenna 126-2 is separated into the versions 404-1 and 404-2 via thefeed ports 402-1 and 402-2. Using the digital mixers 618-1 and 618-2 andthe transmit signal 634, the receivers 604-1 and 604-2 demodulate theradar receive signal 210 and produce the receive signals 622-1 and622-2, respectively.

At least one of the receive signals 622-1 and 622-2 includes a beatfrequency, which is indicative of a frequency offset between the radartransmit signal 208 and the radar receive signal 210. The beat frequencyis proportional to a range to the object 206. The mutual couplingcancellation module 122 performs the mutual coupling cancellation 410 ofFIG. 4 and generates a decoupled signal 624 based on the receive signals622-1 and 622-2. The mutual coupling cancellation module 122 processesthe receive signals 622-1 and 622-2 in such a way as to attenuate themutual coupling signal 216 and enable the beat frequency to be detected.In this way, the decoupled signal 624 substantially includes thereflected component or beat frequency and omits or filters a mutualcoupling component that is associated with the mutual coupling signal216.

In FIG. 6, the processor 124 includes at least one proximity detectionmodule 626 and at least one transmitter (Tx) control module 628. Theproximity detection module 626 obtains the decoupled signal 624 andgenerates detection data 630, which indicates whether or not the object206 is detected. The detection data 630 can also include a range to theobject 206.

Based on the detection data 630, the transmitter control module 628generates at least one transmission parameter 632 that controls one ormore transmission attributes for wireless communication. Thetransmission parameter 632 can specify one or more transmission-relatedaspects of the uplink signal 202, such as a power level, polarization,frequency, duration, beam shape, beam steering angle, a selected antennathat transmits the uplink signal 202 (e.g., another antenna that is on adifferent surface of the computing device 102 and is not obstructed bythe object 206), or combinations thereof. Some transmission parameters632 may be associated with beam management, such as those that define anunobstructed volume of space for beam sweeping. By specifying thetransmission parameter 632, the processor 124 can, for example, causethe transmitter 602 to decrease power if an object 206 is close to thecomputing device 102 or increase power if the object 206 is at a fartherrange or is not detectable. The ability to detect the object 206 andcontrol the transmitter 602 enables the processor 124 to balance theperformance of the computing device 102 with regulatory complianceguidelines. In other implementations, the application processor 108 canperform one or more of these functions.

Although not explicitly shown, multiple antennas 126 can be used tosense additional versions 404 of the radar receive signal 210 (e.g., athird version or a fourth version) and provide additional receivesignals 622 to the mutual coupling cancellation module 122 (e.g., athird receive signal 622 or a fourth receive signal 622). For example,two or more of the patch antennas 416 of FIG. 5 may be used to receivethe radar receive signal 210. In this way, additional information can beprovided to the mutual coupling cancellation module 122 to improve themutual coupling cancellation 410. The mutual coupling cancellationmodule 122 can also generate multiple decoupled signals 624 associatedwith different pairs of receive signals 622 to increase a probability ofdetecting the object 206 (or accurately determining a range thereof) orto decrease a probability of false alarms. The transmitter controlmodule 628 can also make different adjustments based on which antennas126 or what quantity of antennas 126 detect the object 206. In somecases, these adjustments may impact beam management by focusingavailable beams or targeting a spatial area for beam determination.

For example, in some situations, the object 206 may be closer to one ofthe antennas 126 than another, which enables the one antenna 126 todetect the object 206 while the other antenna 126 is unable to detectthe object 206. In this case, the transmitter control module 628 candecrease a transmit power of the antenna 126 that detected the object206 relative to the other antenna 126. In some implementations, themultiple antennas 126 can be used to further characterize therelationship between the object 206 and the antennas 126, such as byusing triangulation to estimate an angle to the object 206. In this way,the transmitter control module 628 can adjust the transmission parameter632 to steer the uplink signal 202 away from the object 206.

Although the wireless transceiver 120 is shown as a direct-conversiontransceiver in FIG. 6, the described techniques can also be applied toother types of transceivers, such as superheterodyne transceivers. Ingeneral, the mutual coupling cancellation module 122 can provideinterference cancellation between any two or more receive signals 622.Operations of the mutual coupling cancellation module 122 are furtherdescribed with respect to FIGS. 7-9.

FIG. 7 illustrates an example scheme performed by a mutual couplingcancellation module 122 for proximity detection using adaptive mutualcoupling cancellation. The mutual coupling cancellation module 122obtains the receive signals 622-1 and 622-2. At 700-1, the receivesignal 622-1 or 622-2 is represented by a vector, which includes amutual coupling component 702 and a reflected component 704. The mutualcoupling component 702 results from the mutual coupling between theantennas 126 (e.g., the mutual coupling signal 216 of FIG. 2) while thereflected component 704 results from the object 206 reflecting the radartransmit signal 208 (e.g., the reflected signal 218 of FIG. 2). Thereflected component 704 contains information about the object 206 (e.g.,the beat frequency) that enables the range to the object 206 to bedetermined. In general, the receive signals 622-1 and 622-2 can berespectively represented by y_(n) ¹ and y_(n) ² according to Equation 1,below:

y _(n) ^(x) =A _(MC) h _(MC) ^(x) s _(MC)(n)+α_(R) h _(R) ^(x) s_(R)(n)+n _(x)  Equation 1

where n represents a discrete time interval, x represents differentresponses of the antenna 126 to the radar receive signal 210 (e.g., theversion 404-1 or the version 404-2 as shown in FIG. 4 or 6), A_(MC) andα_(R) represent the respective amplitudes of the mutual couplingcomponent 702 and the reflected component 704, s_(MC) and s_(R)represent respective complex sinusoidal signals of the mutual couplingcomponent 702 and the reflected component 704, h_(MC) and h_(R)represent respective channel coefficients associated with a mutualcoupling channel and a reflection channel, and n_(x) representsindependent additive white gaussian noise (AWGN). In general, thechannel coefficients are unknown without a training procedure orcalibration process and can vary over time. The receive signals 622-1and 622-2 can be processed as a 2×1 matrix as shown in Equation 2:

$\begin{matrix}\begin{matrix}{\overset{\_}{y} = {{{A_{MC}\begin{bmatrix}h_{MC}^{1} \\h_{MC}^{2}\end{bmatrix}}{s_{MC}(n)}} + {{\alpha_{R}\begin{bmatrix}h_{R}^{1} \\h_{R}^{2}\end{bmatrix}}{s_{R}(n)}} + \begin{bmatrix}n_{1} \\n_{2}\end{bmatrix}}} \\{= {{A_{MC}\overset{\_}{h_{MC}}{s_{MC}(n)}} + {\alpha_{R}\overset{\_}{h_{R}}{s_{R}(n)}} + \overset{\_}{n}}}\end{matrix} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Two properties of the mutual coupling component 702 enable the describedtechniques to cancel (e.g., remove, suppress, attenuate, or filter) themutual coupling component 702 without explicit knowledge of the mutualcoupling channel coefficients (h_(MC) ). A first property includes themutual coupling component 702 being several orders of magnitude largerthan the reflected component 704

$\left( {{e.\; g.},{\frac{A_{MC}^{2}}{\alpha_{R}^{2}} > {25\mspace{14mu} {dB}}}} \right).$

A second property includes the respective mutual coupling components 702in the receive signals 622-1 and 622-2 being highly correlated. Thestrength and correlation of the mutual coupling components 702 enablesthe mutual coupling cancellation module 122 to produce at least onedecoupled signal 624 that substantially includes the reflected component704. In other words, a power of the mutual coupling component 702 issuppressed within the decoupled signal 624 relative to powers of themutual coupling component 702 respectively within the two receivesignals 622-1 and 622-2.

The mutual coupling cancellation module 122 can be implemented using,for example, a zero-forcing combiner module 710 or a reciprocalcancellation module 712 (including both modules). The zero-forcingcombiner module 710 suppresses the mutual coupling component 702 bycombining interference null-space projections of the two receive signals622-1 and 622-2 to generate the decoupled signal 624. This technique isdescribed in further detail with respect to FIG. 8. The zero-forcingcombiner module 710 is relatively easy to scale to more than two receivesignals 622, which can be provided via more than two feed ports 402 ofone or more antennas. Additional receive signals 622 provide additionalinformation to the zero-forcing combiner module 710, which furtherimproves the determination of the orthogonal direction and suppressionof the mutual coupling component 702. The zero-forcing combiner module710 can be implemented in hardware (e.g., via an integrated circuit) orsoftware (e.g., as computer executable instructions stored in thecomputer-readable storage medium 110 and executed by the processor 124).In some implementations, a software implementation is utilized if themutual coupling cancellation module 122 is to process larger quantitiesof receive signals 622 (e.g., more than four receive signals 622).

The reciprocal cancellation module 712 can also generate the decoupledsignal 624. To do so, the reciprocal cancellation module 712 subtracts ascaled version of one of the receive signals 622-1 or 622-2 from anotherof the receive signals 622-1 or 622-2 to generate the decoupled signal624. The reciprocal cancellation module 712 determines the appropriatescaling by using a least squares adaptation criteria and minimizing themean-square error. This technique is described in further detail withrespect to FIG. 9. Similar to the zero-forcing combiner module 710, thereciprocal cancellation module 712 may also be implemented in hardwareor software. In some cases, the reciprocal cancellation module 712 maybe less complex (e.g., may perform fewer computations) relative to thezero-forcing combiner module 710 to generate a given decoupled signal624.

The zero-forcing combiner module 710 or the reciprocal cancellationmodule 712 decouple the mutual coupling component 702 and the reflectedcomponent 704 without explicit knowledge of the mutual coupling channelcoefficient shown in Equation 1. In some cases, a portion of the energyassociated with the reflected component 704 may be lost. Any change tothe reflected component 704, however, is relatively minor compared tothe suppression of the mutual coupling component 702 such that thedecoupled signal 624 can still be used to detect the object 206 anddetermine the range to the object 206.

In some cases, the mutual coupling cancellation module 122 can includeboth the zero-forcing combiner module 710 and the reciprocalcancellation module 712 and enable either technique to generate thedecoupled signal 624. Accordingly, the mutual coupling cancellationmodule 122 may toggle (e.g., switch) between using the zero-forcingcombiner 710 or the reciprocal cancellation module 712. The toggling canoccur based on, for example, a quantity of receive signals 622 that areprovided to the mutual coupling cancellation module 122 (e.g., aquantity of feed ports 402 that are used to receive the radar receivesignal 210), computational ability of the processor 124, and so forth.For instance, the zero-forcing combiner module 710 or the reciprocalcancellation module 712 can respectively be employed if more than tworeceive signals 622 or if two receive signals 622 are provided to themutual coupling cancellation module 122.

Alternatively, the mutual coupling cancellation module 122 can enableboth the zero-forcing combiner 710 and the reciprocal cancellationmodule 712 to operate in parallel to generate two decoupled signals 624.The proximity detection module 626 of FIG. 6 can use the multipledecoupled signals 624 to improve an accuracy of the detection data 630or reduce false alarms. The zero-forcing combiner module 710 and thereciprocal cancellation module 712 are further described with respect toFIGS. 8 and 9, respectively.

FIG. 8 illustrates an example scheme performed by a zero-forcingcombiner module 710 for proximity detection using adaptive mutualcoupling cancellation. The zero-forcing combiner module 710 includes acovariance module 802, an eigenvector decomposition module 804, aneigenvector selection module 806, and a null-space projection module808. In general, the zero-forcing combiner module 710 determines one ormore weights 810 (e.g., filter coefficients) that project the receivesignals 622-1 and 622-2 onto an interference null-space (e.g., adirection that is orthogonal to the mutual coupling component 702). At700-2, a mutual coupling direction is shown via MC direction 818 and adirection that is orthogonal to the mutual coupling direction is shownas orthogonal direction 820. The weights 810 are chosen to minimize aninterference over noise ratio at an output of the zero-forcing combinermodule 710.

The covariance module 802 obtains the receive signals 622-1 and 622-2and generates a covariance matrix (R_(yy) ) 812. The eigenvectordecomposition module 804 determines the eigenvector decomposition of thecovariance matrix 812 and generates eigenvector decomposition data 814,which includes eigenvalues and eigenvectors. The resulting operations ofthe covariance module 802 and the eigenvector decomposition module 804are shown in Equation 3 below:

R _(yy) =E[ y y ^(T)]=Σ_(i=1) ^(r)λ_(i) v _(i) {circumflex over (v)}r_(i) ^(T)  Equation 3

where E[ ] represents an expected value function, the exponent ^(T)represents a matrix transform operation, r represents a quantity ofreceive signals 622—which is two in this example, λ_(i) represents aneigenvalue, vi represents an eigenvector, and y is represented inEquation 2.

Based on the eigenvector decomposition data 814, the eigenvectorselection module 806 selects an eigenvector that is associated with asmallest eigenvalue. Because the mutual coupling component 702 issignificantly stronger than the reflected component 704 and iscorrelated between the receive signals 622-1 and 622-2, one of theeigenvalues is significantly stronger than the other eigenvalue. Thus,an eigenvector associated with the stronger eigenvalue is correlated tothe mutual coupling direction 818, and an eigenvector associated withthe weaker eigenvalue is correlated to the orthogonal direction 820.Based on these correlations, the eigenvector selection module 806generates the weights 810 based on the eigenvector associated with thesmallest eigenvalue. The null-space projection module 808 applies theweights 810 to the receive signals 622-1 and 622-2 using amultiplication operation to generate the projected signals 816-1 and816-2. The projected signal 816-1 or 816-2 is shown at 700-2 as theprojection of receive signal 622-1 or 622-2 onto the orthogonaldirection 820. As illustrated in 700-2, the projected signal 816-1 or816-2 substantially includes the reflected component 704. The null-spaceprojection module 808 sums the projected signals 816-1 and 816-2together to generate the decoupled signal 624.

The zero-forcing combiner module 710 can also be easily scaled toprocess more than two receive signals 622. In some cases, three, four,or more receive signals 622 can be provided to the covariance module802, which increases a dimensional size of the covariance matrix 812 andincreases a quantity of computations to generate the eigenvectordecomposition data 814. Although there are more than two eigenvalues andeigenvectors in this situation, the eigenvector selection module 806selects the eigenvector associated with a smallest eigenvalue and theresulting projected signals 816 are combined by the null-spaceprojection module 808 to produce the decoupled signal 624.

FIG. 9 illustrates an example scheme performed by a reciprocalcancellation module 712 for proximity detection using adaptive mutualcoupling cancellation. The reciprocal cancellation module 712 includes acovariance module 902, a cross-correlation module 904, a least-squaresmodule 906, and a filter cancellation module 908. In general, thereciprocal cancellation module 712 uses least-squares approximation todetermine at least one weight 910 (e.g., filter coefficient or complexweight) that scales a magnitude or phase of one of the receive signals622-1 or 622-2 such that the mutual coupling component 702 in anotherone of the receive signals 622-1 or 622-2 can be canceled. In thedepicted configuration, the receive signal 622-2 is scaled to produce ascaled signal 914, as described below. Because the mutual couplingcomponent 702 is the dominant component, the weight 910 is chosen tominimize a mean-squared error between the receive signal 622-1 and thescaled version of the receive signal 622-2.

The covariance module 902 obtains the receive signals 622-1 and 622-2and generates a covariance matrix (R_(yy) ) 812, as described above inEquation 3. The cross-correlation module 904 obtains the receive signals622-1 and 622-2 and generates a cross-correlation matrix (r_(yy) ) 912.Using the covariance matrix 812 and the cross-correlation matrix 912,the least-squares module 906 generates the weight 910 according toEquation 4 below:

w=(R _(yy))⁻¹ r _(yy)  Equation 4

The filter cancellation module 908 multiples the receive signal 622-2with the weight 910 to generate the scaled signal 914. The scaled signal914 is subtracted from the receive signal 622-1 to generate thedecoupled signal 624. Alternatively, the scaled signal 914 can beinverted and added to the receive signal 622-1 to generate the decoupledsignal 624. An inverse of the scaled signal 914 is shown at 700-3, whichis approximately equal in magnitude to the mutual coupling component 702and approximately 180 degrees out of phase with respect to the mutualcoupling component 702. If the other receive signal 622-1 or 622-2 iscombined with the inverse of the scaled signal 914, the mutual couplingcomponent 702 is effectively cancelled and the resulting decoupledsignal 624 substantially includes the reflected component 704.

FIGS. 10-1, 10-2, 11-1, and 11-2 illustrate flow diagrams of exampleprocesses 1000-1, 1000-2, 1100-1, and 1100-2, respectively, forproximity detection using adaptive mutual coupling cancellation. Theprocesses 1000-1, 1000-2, 1100-1, and 1100-2 are respectively describedin the form of sets of blocks 1002-1006, 1008-1014, 1102-1106, and1108-1114 that specify operations that can be performed. The operations,however, are not necessarily limited to the order shown in FIG. 10-1,10-2, 11-1, or 11-2 or described herein, for the operations may beimplemented in alternative orders or in fully or partially overlappingmanners. Operations represented by the illustrated blocks of theprocesses 1000-1, 1000-2, 1100-1, or 1100-2 may be performed, forexample, by a computing device 102 (e.g., of FIG. 1 or 2) or a wirelesstransceiver 120 (e.g., of FIG. 1 or 6). More specifically, theoperations of the processes 1000-1, 1000-2, 1100-1, or 1100-2 may beperformed by a mutual coupling cancellation module 122 or a processor124 as shown in FIG. 1 or 6.

With respect to the process 1000-1 illustrated in FIG. 10-1, a radartransmit signal is transmitted via a first antenna at 1002. As shown inFIG. 6, the wireless transceiver 120 provides the first antenna 126-1the radar transmit signal 208, which may comprise a frequency-modulatedcontinuous wave signal or a frequency-modulated pulsed signal.

At 1004, multiple versions of a radar receive signal are received viamultiple feed ports of at least a second antenna that is mutuallycoupled electromagnetically to the first antenna. As described withrespect to FIG. 5, one or more antennas 126 can receive the radarreceive signal 210 via feed ports 402-1 and 402-2. The radar receivesignal 210 is based on the radar transmit signal 208 and may include themutual coupling signal 216 and the reflected signal 218, as shown inFIGS. 2, 4, and 6.

At 1006, a decoupled signal is generated based on the multiple versionsof the radar receive signal. As shown in FIG. 6, the mutual couplingcancellation module 122 generates the decoupled signal 624 based on thereceive signals 622-1 and 622-2, which are respectively associated withfeed ports 402-1 and 402-2. The decoupled signal 624 can be generatedusing the zero-forcing combiner module 710 or the reciprocalcancellation module 712, as illustrated in FIG. 7.

With respect to the process 1000-2 illustrated in FIG. 10-2, a radartransmit signal is transmitted via a first antenna at 1008. For example,the wireless transceiver 120 can transmit the radar transmit signal 208using the first antenna 126-1, as shown in FIG. 6. The first antenna126-1 may be implemented as any type of antenna, including a dipoleantenna 412, a patch antenna 416, or a bowtie antenna 420 as shown inFIG. 4. The first antenna 126-1 can transmit the radar transmit signal208 via one or more feed ports, including the differential feed ports414, the polarized feed ports 418, or the directional feed ports 422. Insome cases, multiple antennas 126 are used to transmit the radartransmit signal 208, as described with respect to FIG. 5.

At 1010, multiple versions of a radar receive signal are received viamultiple feed ports including at least one feed port of a secondantenna. The wireless transceiver 120, for example, can receive twoversions 404-1 and 404-2 of the radar receive signal 210 using feedports 402-1 and 402-2 of the second antenna 126-2, as shown in FIGS. 4and 6. The first antenna 126-1 and the second antenna 126-2 are mutuallycoupled electromagnetically. The first antenna 126-1 and the secondantenna 126-2 may be indirectly coupled due to relative proximity, asshown in FIG. 2. In some cases, one or more of the antennas 126, such asthe first antenna 126-1 and the second antenna 126-2, may compriseantenna elements within the antenna array 212.

Here, the radar receive signal comprises a reflected componentcorresponding to a reflection of the radar transmit signal via an objectand a mutual coupling component corresponding to a transmission of theradar transmit signal via the first antenna. As shown in FIG. 2, theradar receive signal 210 includes the reflected signal 218 and themutual coupling signal 216, which are respectively represented by thereflected component 704 and the mutual coupling component 702 in FIG. 7.

The second antenna 126-2 may be implemented as any type of antenna,including a dipole antenna 412, a patch antenna 416, or a bowtie antenna420 as shown in FIG. 4. The second antenna 126-2 can receive themultiple versions 404 of the radar receive signal 210 via thedifferential feed ports 414, the polarized feed ports 418, or thedirectional feed ports 422. In some cases, multiple antennas 126 areused to receive the multiple versions 404 of the radar receive signal210, as described with respect to FIG. 5.

At 1012, a decoupled signal is generated by processing the multipleversions of the radar receive signal such that the mutual couplingcomponent is attenuated. For example, the mutual coupling cancellationmodule 122 of FIG. 1, 6, or 7 can generate the decoupled signal 624 byprocessing the multiple receive signals 622, which are derived from themultiple versions 404 of the radar receive signal 210, to attenuate themutual coupling component 702. The mutual coupling cancellation module122 can use the zero-forcing combiner module 710 or the reciprocalcancellation module 712 to combine the multiple receive signals 622, asdescribed with respect to FIGS. 7, 8 and 9.

At 1014, a transmission parameter is adjusted based on the decoupledsignal, with the transmission parameter varying according to a range tothe object. The transmitter control module 628, for example, can adjustthe transmission parameter 632 based on the decoupled signal 624, asshown in FIGS. 3 and 6. Example transmission parameters 632 include abeam steering angle, a frequency, a communication protocol, a selectedantenna or antenna array, a transmit power level, and so forth. Thetransmission parameter 632 can be varied according to a range of theobject 206. For instance, a transmit power level may be increased forgreater ranges to the object 206 and decreased for smaller ranges to theobject 206. In some cases, the transmission parameter 632 isincrementally adjusted as the object 206 moves towards or away from thecomputing device 102 over time.

With respect to the process 1100-1 illustrated in FIG. 11-1, radiationis generated via a first antenna at 1102. For example, the first antenna126-1 can generate radiation by transmitting the radar transmit signal208, which is provided by the wireless transceiver 120.

At 1104, multiple versions of a radio-frequency signal are generated viamultiple feed ports of at least a second antenna. As shown in FIGS. 4and 6, the feed ports 402-1 and 402-2 generate the multiple versions404-1 and 404-2 of the radar receive signal 210. The feed ports 402-1and 402-2 may be associated with the second antenna 126-2 or differentantennas 126, as described with respect to FIG. 5.

At 1106, interference generated by the first antenna is attenuated usingthe multiple versions of the radio-frequency signal. The interference isrepresented via the mutual coupling component 702. The mutual couplingcancellation module 122 attenuates the mutual coupling component 702using the multiple versions 404-1 and 404-2. In some cases, more thantwo versions 404 of the radar receive signal 210 may be used toattenuate the interference.

With respect to the process 1100-2 illustrated in FIG. 11-2, radiationis generated via a first antenna at 1108. For example, the first antenna126-1 can generate radiation by transmitting the radar transmit signal208 provided by the wireless transceiver 120.

At 1110, multiple versions of a radio-frequency signal are generated viamultiple feed ports of at least a second antenna. The first antenna andthe second antenna are mutually coupled electromagnetically. Themultiple versions of the radio-frequency signal include interferenceindicative of the radiation generated by the first antenna. For example,the second antenna 126-2 can generate the multiple versions 404 of theradar receive signal 210, which is a type of radio-frequency signal.

At 1112, interference null-space projections of the multiple versions ofthe radio-frequency signal are combined to attenuate the interference.For example, the zero-forcing combiner module 710 can project thereceive signals 622-1 and 622-2, which are derived from the multipleversions 404 of the radar receive signal 210, onto the orthogonaldirection 820 to produce the projected signals 816-1 and 816-2, as shownin FIG. 8. The zero-forcing combiner module 710 can then sum theprojected signals 816-1 and 816-2 together to produce the decoupledsignal 624. By projecting the receive signals 622-1 and 622-2 onto theorthogonal direction 820, the respective mutual coupling components 702are suppressed.

At 1114, a version of the multiple versions of the radio-frequencysignal is scaled to produce a scaled signal, and the scaled signal issubtracted from another version of the multiple versions of theradio-frequency signal to attenuate the interference. For example, thereciprocal cancellation module 712 can subtract the scaled signal 914from the receive signal 622-1, as shown in FIG. 9. The scaled signal 914can be derived from the receive signal 622-2. The receive signals 622-1and 622-2 are respectively derived from the multiple versions 404 of theradar receive signal 210. By subtracting the scaled signal 914 from thereceive signal 622-1, the mutual coupling component 702 in the receivesignal 622-1 is suppressed. The operations described at 1112 and 1114can be performed in sequence, in parallel, or in lieu of one another.

Unless context dictates otherwise, use herein of the word “or” may beconsidered use of an “inclusive or,” or a term that permits inclusion orapplication of one or more items that are linked by the word “or” (e.g.,a phrase “A or B” may be interpreted as permitting just “A,” aspermitting just “B,” or as permitting both “A” and “B”). Further, itemsrepresented in the accompanying figures and terms discussed herein maybe indicative of one or more items or terms, and thus reference may bemade interchangeably to single or plural forms of the items and terms inthis written description. Finally, although subject matter has beendescribed in language specific to structural features or methodologicaloperations, it is to be understood that the subject matter defined inthe appended claims is not necessarily limited to the specific featuresor operations described above, including not necessarily being limitedto the organizations in which features are arranged or the orders inwhich operations are performed.

What is claimed is:
 1. An apparatus comprising: at least two antennas,the at least two antennas including a first antenna and a secondantenna, the second antenna including two feed ports, the first antennaand the second antenna mutually coupled electromagnetically; a wirelesstransceiver connected to the at least two antennas, the wirelesstransceiver configured to: transmit a radar transmit signal via thefirst antenna; receive two versions of a radar receive signalrespectively via the two feed ports of the second antenna, the radarreceive signal comprising a reflected component corresponding to areflection of the radar transmit signal via an object and a mutualcoupling component corresponding to a transmission of the radar transmitsignal via the first antenna; and adjust a transmission parameter basedon a decoupled signal, the transmission parameter varying based on arange to the object; and a mutual coupling cancellation module connectedto the two feed ports, the mutual coupling cancellation moduleconfigured to generate the decoupled signal based on the two versions ofthe radar receive signal.
 2. The apparatus of claim 1, wherein themutual coupling cancellation module is configured to generate thedecoupled signal such that a power of the mutual coupling component issuppressed within the decoupled signal relative to powers of the mutualcoupling component respectively within the two versions of the radarreceive signal.
 3. The apparatus of claim 1, wherein the radar transmitsignal comprises: a frequency-modulated continuous-wave (FMCW) signal;or a frequency-modulated pulsed signal.
 4. The apparatus of claim 1,wherein: the wireless transceiver is configured to: generate a digitaltransmit signal, the radar transmit signal derived from the digitaltransmit signal; generate two digital receive signals, the two digitalreceive signals respectively derived from the two versions of the radarreceive signal; and mix the digital transmit signal with the two digitalreceive signals to respectively produce two receive signals; and themutual coupling cancellation module is configured to generate thedecoupled signal based on the two receive signals.
 5. The apparatus ofclaim 4, wherein: the two receive signals include a respective beatfrequency indicative of a frequency offset between transmission of theradar transmit signal and reception of the radar receive signal, therespective beat frequency proportional to the range to the object; andthe mutual coupling cancellation module is configured to generate thedecoupled signal to include the beat frequency.
 6. The apparatus ofclaim 4, wherein the mutual coupling cancellation module includes azero-forcing combiner, the zero-forcing combiner configured to combineinterference null-space projections of the two receive signals togenerate the decoupled signal.
 7. The apparatus of claim 6, wherein thezero-forcing combiner is configured to: generate a covariance matrixbased on the two receive signals; perform eigenvector decomposition onthe covariance matrix to generate eigenvectors and eigenvalues; generateone or more weights based on an eigenvector of the eigenvectors that isassociated with a smallest eigenvalue of the eigenvalues; project thetwo receive signals by multiplying the two receive signals by the one ormore weights to generate two projected signals; and perform a summationof the two projected signals to generate the decoupled signal.
 8. Theapparatus of claim 4, wherein the mutual coupling cancellation moduleincludes a reciprocal cancellation module, the reciprocal cancellationmodule configured to subtract a scaled version of a signal of the tworeceive signals from another signal of the two receive signals togenerate the decoupled signal.
 9. The apparatus of claim 8, wherein thereciprocal cancellation module is configured to: generate a covariancematrix based on the two receive signals; generate a cross-correlationmatrix based on the two receive signals; perform least squaresapproximation of the signal with respect to the other signal based onthe covariance matrix and the cross-correlation matrix to produce atleast one weight; multiply the signal by the at least one weight togenerate a scaled signal; and subtract the scaled signal from the othersignal to generate the decoupled signal.
 10. The apparatus of claim 1,wherein the at least two antennas are configured to be arranged inrespective positions such that the first antenna and the second antennaare mutually coupled electromagnetically.
 11. The apparatus of claim 1,wherein: the at least two antennas include a third antenna, the thirdantenna including a third feed port, the first antenna and the thirdantenna mutually coupled electromagnetically; and the wirelesstransceiver is connected to the third antenna and is configured toobtain the two versions of the radar receive signal respectively via afeed port of the two feed ports of the second antenna and via the thirdfeed port of the third antenna.
 12. The apparatus of claim 1, wherein:the at least two antennas include a third antenna, the third antennaincluding a third feed port, the first antenna and the third antennamutually coupled electromagnetically, wherein: the wireless transceiveris connected to the third antenna and is configured to respectivelyobtain three versions of the radar receive signal via each of the twofeed ports of the second antenna and via the third feed port of thethird antenna; and the mutual coupling cancellation module is configuredto generate the decoupled signal based on the three versions of theradar receive signal such that a power of the mutual coupling componentis suppressed within the decoupled signal relative to the powers of themutual coupling component respectively within the three versions of theradar receive signal.
 13. The apparatus of claim 1, wherein the wirelesstransceiver is configured to transmit an uplink signal using thetransmission parameter.
 14. The apparatus of claim 1, wherein thetransmission parameter comprises at least one of the following: a powerlevel; a beam steering angle; a frequency; a selected antenna; or acommunication protocol.
 15. The apparatus of claim 1, wherein: the firstantenna comprises one of the following: a patch antenna including ahorizontally-polarized feed port and a vertically-polarized feed port; adipole antenna including differential feed ports; or a bowtie antennaincluding directional feed ports.
 16. The apparatus of claim 15, whereinthe wireless transceiver is configured to transmit the radar transmitsignal using: at least one of the horizontally-polarized feed port orthe vertically-polarized feed port of the patch antenna; at least one ofthe differential feed ports of the dipole antenna; or at least one ofthe directional feed ports of the bowtie antenna.
 17. The apparatus ofclaim 1, wherein: the second antenna comprises one of the following: apatch antenna including a horizontally-polarized feed port and avertically-polarized feed port; a dipole antenna including differentialfeed ports; or a bowtie antenna including directional feed ports; andthe wireless transceiver is configured to produce the two versions ofthe radar receive signal using: the horizontally-polarized feed port andthe vertically-polarized feed port of the patch antenna; thedifferential feed ports of the dipole antenna; or the directional feedports of the bowtie antenna.
 18. An apparatus comprising: at least twoantennas, the at least two antennas including a first antenna and asecond antenna, the first antenna and at least the second antennamutually coupled electromagnetically; a wireless transceiver connectedto the at least two antennas, the wireless transceiver configured to:transmit a radar transmit signal via the first antenna; receive multipleversions of a radar receive signal via multiple feed ports including atleast one feed port of the second antenna, the radar receive signalcomprising a reflected component corresponding to a reflection of theradar transmit signal via an object and a mutual coupling componentcorresponding to a transmission of the radar transmit signal via thefirst antenna; and adjust a transmission parameter based on a decoupledsignal, the transmission parameter varying based on a range to theobject; and a mutual coupling cancellation circuit connected to themultiple feed ports, the mutual coupling cancellation circuit configuredto generate the decoupled signal based on the multiple versions of theradar receive signal such that the mutual coupling component issuppressed.
 19. The apparatus of claim 18, wherein: the second antennaincludes a first feed port and a second feed port; the at least twoantennas include a third antenna, the third antenna includes a thirdfeed port, the first antenna and the third antenna are mutually coupledelectromagnetically; and the wireless transceiver is connected to thethird antenna and is configured to: receive the multiple versions of theradar receive signal respectively via the first feed port of the secondantenna and the third feed port of the third antenna; or receive themultiple versions of the radar receive signal respectively via the firstfeed port of the second antenna, the second feed port of the secondantenna, and the third feed port of the third antenna.
 20. The apparatusof claim 18, wherein: the wireless transceiver is configured to generatetwo receive signals, the two receive signals respectively comprising twodigital signals derived from the multiple versions of the radar receivesignal; and the mutual coupling cancellation circuit is configured tocombine the two receive signals to generate the decoupled signal suchthat a power of the mutual coupling component is suppressed within thedecoupled signal relative to powers of the mutual coupling componentrespectively within the two receive signals.
 21. The apparatus of claim20, wherein the mutual coupling cancellation circuit comprises azero-forcing combiner circuit configured to combine interferencenull-space projections of the two receive signals to generate thedecoupled signal.
 22. The apparatus of claim 21, wherein thezero-forcing combiner circuit is configured to: generate a covariancematrix based on the two receive signals; perform eigenvectordecomposition on the covariance matrix to generate eigenvectors andeigenvalues; generate one or more weights based on an eigenvector of theeigenvectors that is associated with a smallest eigenvalue of theeigenvalues; project the two receive signals by multiplying the tworeceive signals by the one or more weights to generate two projectedsignals; and perform a summation of the two projected signals togenerate the decoupled signal.
 23. The apparatus of claim 20, whereinthe mutual coupling cancellation circuit comprises a reciprocalcancellation circuit configured to subtract a scaled version of a signalof the two receive signals from another signal of the two receivesignals to generate the decoupled signal.
 24. The apparatus of claim 23,wherein the reciprocal cancellation circuit is configured to: generate acovariance matrix based on the two receive signals; generate across-correlation matrix based on the two receive signals; perform leastsquares approximation of the signal with respect to the other signalbased on the covariance matrix and the cross-correlation matrix toproduce at least one weight; multiply the signal by the at least oneweight to generate a scaled signal; and subtract the scaled signal fromthe other signal to generate the decoupled signal.
 25. A method forproximity detection using adaptive mutual coupling cancellation, themethod comprising: transmitting a radar transmit signal via a firstantenna; receiving multiple versions of a radar receive signal viamultiple feed ports including at least one feed port of a secondantenna, the first antenna and the second antenna mutually coupledelectromagnetically, the radar receive signal comprising a reflectedcomponent corresponding to a reflection of the radar transmit signal viaan object and a mutual coupling component corresponding to atransmission of the radar transmit signal via the first antenna;generating a decoupled signal by processing the multiple versions of theradar receive signal such that the mutual coupling component isattenuated; and adjusting a transmission parameter based on thedecoupled signal, the transmission parameter varying according to arange to the object.
 26. The method of claim 25, wherein the generatingof the decoupled signal comprises at least one of the following:combining interference null-space projections of the multiple versionsof the radar receive signal to generate the decoupled signal; orsubtracting a scaled signal from a version of the multiple versions ofthe radar receive signal to generate the decoupled signal, the scaledsignal derived from another version of the multiple versions of theradar receive signal.
 27. The method of claim 26, further comprisingtoggling between at least the combining of the interference null-spaceprojections and the subtracting of the scaled signal to generate thedecoupled signal based on a quantity of the multiple versions of theradar receive signal.
 28. An apparatus comprising: at least twoantennas, the at least two antennas including: a first antennaconfigured to generate radiation; and a second antenna includingmultiple feed ports, the first antenna and the second antenna mutuallycoupled electromagnetically, the second antenna configured to generatemultiple versions of a radio-frequency signal respectively via themultiple feed ports, the multiple versions of the radio-frequency signalincluding interference indicative of the radiation generated by thefirst antenna; and a mutual coupling cancellation module connected tothe multiple feed ports, the mutual coupling cancellation moduleincluding: a zero-forcing combiner module configured to combineinterference null-space projections of the multiple versions of theradio-frequency signal to attenuate the interference; and a reciprocalcancellation module configured to: scale a version of the multipleversions of the radio-frequency signal to produce a scaled signal; andsubtract the scaled signal from another version of the multiple versionsof the radio-frequency signal to attenuate the interference.
 29. Theapparatus of claim 28, wherein the mutual coupling cancellation moduleis configured to enable the zero-forcing combiner module and thereciprocal cancellation module to operate in parallel using the multipleversions of the radio-frequency signal.
 30. The apparatus of claim 28,wherein the mutual coupling cancellation module is configured to enablethe zero-forcing combiner module or the reciprocal cancellation modulebased on a quantity of the multiple versions of the radio-frequencysignal.